Where r u? That text message, says Sam Altman, was so common that he wanted to find a way to answer it – for everyone.

As a sophomore in computer science at Stanford University, Mr. Altman imagined a way that mobile phone users could seamlessly check their friends’ whereabouts with location-tracking technology. But back in 2005, global positioning system (GPS) hadn’t arrived in smart phones.

Technology soon caught up with the idea. Today his company, Loopt, has more than 1 million users and is one of the most popular services to allow people to track their friends via their smart phones. And with more cellphones now equipped with GPS, other services such as Google Latitude are collecting location data from scores of users and broadcasting that information through phone networks or the Internet.

Such tracking services offer a great way for people stay connected – and can be a boon for parents – but their proliferation also has privacy advocates biting their nails. As companies forge into largely uncharted areas of tracking and recording customer locations, many worry that consumers won’t be able to ensure that their private information – such as their whereabouts on a given day – is being safeguarded, especially from advertisers.

Ms. Gelman and other privacy experts caution that when users allow companies to track their locations, third parties – such as the government, litigants, and advertisers – can potentially tap into that data. “If you have the information, someone is going to come asking for it.”

In other words, could your iPhone or BlackBerry be used to spy on you? Will your spouse or employer know where you are even when you don't want them to?

Who’s in the Loopt?

As Loopt and Google are moving forward in the realm of geosocial or mobile social networking, companies such as NearbyNow and Placecast are exploring ways that advertisers could potentially exploit growing databases of location-specific information (imagine, for instance, getting a coupon for pizza on your mobile phone after walking by a pizzeria).

Altman stresses that Loopt puts a premium on customer privacy and doesn't sell the information to advertisers. It does, however, post ads on its service based on location. Its privacy policy states: “Loopt discloses some personally identifiable, registration, profile, or location information to subsidiaries, affiliated companies, or other businesses or persons for the purpose of providing certain features of the Loopt Services, in order to serve relevant advertisements in support of the Loopt Services, and for processing such information on our behalf.”

When it comes to safety, Loopt gives users control over when to reveal their location and who gets to see it. It also gives them the ability to alter or remove it at any time. While Loopt is built to let people meet up with friends who happen to be nearby, it has a public option in which users reveal their location to a broader group.

The intent of this option, called Loopt Mix, is to allow users to meet other service subscribers in real life.

Loopt advises caution when using this feature: “When meeting up with another Mix user, always meet in a public space with people around. Bring a friend or at least let a friend know where you're going.”

What happens if the service is abused? Altman says the community of Loopt users has proven to be a reliable watchdog. Several users suspected of illicit activity have been reported and kicked off the service, he says.

Services that keep tabs on your every move do seem a bit “creepy,” admits Ryan Calo, a residential fellow at CIS and an expert on electronic privacy issues. But, he says, while they could potentially lead to some criminal wrongdoing, he doesn't think “location based services are going to play into that dynamic.... [I]n the bulk of cases, this tool is going to be used by people who already have a relationship to augment that relationship.”

Some tracking services, for example, allow family members keep track of each other or parents to keep an eye on their children.

Much of what's driving the growth of mobile social networking or geo-locating services, says Mr. Calo, is the fact that "location data is really salient. It really matters to an individual to find things around them and really matters to advertisers to connect with people.”

Laws lag behind

Congress is taking interest in the growth in mobile tracking – and the growth in all sorts of data tracking that’s happening online – and what it means for consumer privacy. At a hearing on communication networks and consumer privacy last week, Loopt chief operating officer Brian Knapp was asked whether the federal government should begin regulating how companies use the private data collected by internet service providers and other companies that gather location information.

“A high-level privacy framework that sticks by tried-and-true principles would be beneficial,” Mr. Knapp told the House panel. But he added that he had concerns that laws could also get “focused on a snapshot in a moment in time and may get outdated.”

“The laws are always years behind technology, says Paul Stephens, director of policy and advocacy at the Privacy Rights Clearinghouse. “These location-tracking services have been available since about 2005 and the laws haven’t caught up with the technology.”

The most important thing, he says, is for new users to be fully informed of the potential consequences when they opt for mobile tracking services. But, “typically they aren’t.”

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